1. Field of the Invention
This invention relates to a method and apparatus for screening therapeutic effects from electrical stimulation of electrically excitable tissue, and more particularly to a portable stimulation device that allows the user to configure the parameters of a respective stimulation signal applied on each of at least one implanted stimulation electrode and that stores ratings of the therapeutic effects along with the corresponding stimulation signal parameters.
2. Description of the Related Art
The use of medical devices for electrical stimulation of electrically excitable tissue is well known in the medical arts. Electrical stimulation of brain tissue has been used for tremor suppression, and electrical stimulation of peripheral nerve tissue has been used to promote blood circulation in patients having peripheral vascular disease. In addition, electrical stimulation of the brain and nerve tissue of the spinal cord has been used for pain management. Electrodes have been implanted near the spinal column of the human body to provide pain relief. The nerve tissue within the spinal column is stimulated electrically to reduce pain sensations at another part of the body.
Depending on the particularities of each different human body, the parameters of the stimulation signals applied near electrically excitable tissue are adjusted to optimize the therapeutic effect from the electrical stimulation. For example for pain management, the area of excitation within the spinal column and the intensity of excitation can be varied by corresponding adjustment of the parameters of the stimulation signals.
In order to vary the area of excitation, an array of electrodes may be implanted near the nerve tissue within the spinal column. Then, each of those electrodes can be configured to have a respective one of a positive or negative polarity or to be in the off-state such that the desired area of the nerve tissue within the spinal column is electrically stimulated. In addition, the amplitude, the pulse width, and the pulse rate of the respective stimulation signal applied on each of those implanted electrodes can be varied for a corresponding variation in area of excitation within the spinal column and in the intensity of excitation.
Deciding how to optimally provide electrical stimulation therapy to any particular individual involves three steps of screening. The first step of screening involves determining whether electrical stimulation of electrically excitable tissue can provide sufficient enough therapeutic effect to be worth implanting the electrodes near the electrically excitable tissue of the patient. The second step of screening involves adjusting the parameters of the respective stimulation signal applied on each of the implanted electrodes to optimize therapeutic effect before those electrodes are implanted for the long-term. The third step of screening involves readjusting the stimulation signal parameters for each of the stimulation electrodes that have been implanted for the long-term to continually optimize therapeutic effect.
In the prior art screening system and method, an array of electrodes is implanted temporarily near the electrically excitable tissue of a patient. Then, a clinician who is knowledgeable of the effects of electrical stimulation would vary the parameters of the respective stimulation signal applied on each of the implanted electrodes. The patient may rate the effectiveness in therapeutic effect for each variation in the parameters of the stimulation signals. If electrical stimulation of electrically excitable tissue does result in a sufficient enough therapeutic effect for the patient, then the electrodes are implanted for the long term with stimulation signals having parameters that lead to optimized therapeutic effect for the particular patient. In addition, by using radio-frequency telemetry with the implantable pulse generator, parameters of the stimulation signals can be adjusted to continually optimize therapeutic effect after the stimulation electrodes have been implanted permanently.
In the prior art screening system and method, the knowledgeable clinician with nonportable equipment performs the screening procedure. As stimulation signals with various parameter settings are applied on the electrodes, the clinician or patient records a rating of therapeutic effect. This procedure can be time-consuming and laborious because of the many possible combinations of parameter settings. U.S. Pat. No. 5,370,672 to Fowler et al. discloses a computer-controlled neurological stimulation system for automating the screening procedure to reduce the time and labor required during screening. However that system, which uses a computer terminal and a graphics drawing tablet, is non-portable and can be expensive.
Because of the non-portability of the prior art screening systems, the clinician and patient spend many hours in a clinical setting. Moreover, because of the non-portability of the prior art screening system, the rating of therapeutic effect under normal daily activities of the user are not available. Thus, a screening system, that is inexpensive and that is adapted to be portable, is desired.